Bake a Displacement map from a cylinder object
Since you're baking scalar displacement from a cylinder, the set-up isn't too bad.. the illustration below shows the rope shaded with its height-map-to-cylinder.

Assuming your rope has its object Z axis straight up its core, with this tree, you put the radial distance from its surface to an (imaginary) cylinder, in this case with radius of 0.65, straight into the strength of a pure-white emission shader.
Put the UV unwrapped low-poly cylinder in the same location as the rope, at the world origin, and bake the emission from selected (the rope), to active (the cylinder) Bake into a floating-point format, 16 bits will probably do.
Then the baked map can drive a Displacement shader for the cylinder:

The cylinder, displaced, is on the left, next to its baked height-map, and the original rope on the right.
It is possible to bake Vector Displacement .. it gets a bit more complicated, with an intermediate map of World-Space positions baked for the Hi-res object, from which positions of the Lo-res object are then subtracted, and baked again, into an exactly corresponding UV map.